Magnetic, transport and electronic structure properties of U 2RuGa 8

Abstract

A single crystal of uranium ternary intermetallic of U 2RuGa 8 was grown by the Ga self-flux method. This compound crystallizes in the tetragonal unit cell of space group P4/mmm. Despite the fairly large U–U shortest distance of 4.22 Å, this compound shows no signs of any magnetic ordering down to 1.9 K. Instead, the susceptibility measured along the a and c axes, goes through a broad maximum at T max = 220 K showing a distinct anisotropy. For j|| a there is a weak temperature dependence of the electrical resistivity with a large value of ρ 0 = 117 μ Ω cm , while for j|| c the ρ ( T ) curve goes through a maximum at about 130 K. The magnetoresistivity measured along two crystallographic directions is small and positive. The thermopower S for the two directions studied is positive and larger along the a-axis. It goes through a broad maximum at 175 K reaching a value of 45 μV/K. The electronic structure has been calculated by the tight-binding linear muffin-tin orbital method (TB-LMTO) and the results were used in calculation of the valence band near the Fermi level compared next to that found in photoemission experiment. The core 4f spectra are also presented. All the above properties are discussed in view of mixed valence behaviour of uranium atom in this compound.